The injection well just south of DFW airport has been out of use
since September 2011, according to Frohlich, but he says that
doesn't rule it out as a cause of the weekend's quakes. He
explained that, though water is no longer being added, lingering
pressure differences from wastewater injection could still be
contributing to the lubrication of long-stuck faults.

"Faults are everywhere. A lot of them are stuck, but if you pump
water in there, it reduces friction and the fault slips a
little,"
Frohlich told Life's Little Mysteries. "I can't prove that
that's what happened, but it's a plausible explanation."